The proposed studies are intended to establish the chemical and physical properties of heparins and heparin-like polysaccharides isolated from neoplastic mast cells which vary in degrees of differentiation. The tumor grading system established with the canine mastocytoma will be used to evaluate the response of dogs with tumors to heparin and histamine. The levels of histamine synthesis, histamine-heparin binding ratios, degree of N-sulfation, and structural properties of mast cell granules and polysaccharides will be related to the formation of vascular lesions, gastric and duodenal ulceration, and the signs of histaminosis. Work on the lymphoproliferative diseases of mustelids will further classify the Aleutian disease virus potentially as a picornavirus. The factors associated with viral chronicity are being studied from the standpoint of antibody affinity, induction of multiple viral forms and immune complex formation. The pathogenesis relating to lack of T-lymphocyte function, immunodeficiency and plasma cell proliferation as the result of virus replication in reticuloendothelial cells will be sought. Lymphoblastic leukemia virus of fowl (JM-V strain of Marek's disease) has been established as a herpes-type virus and will be studied in relationship to other oncogenic herpesviruses. The pathogenesis concerning the transition of what perhaps may be reactive T-cells in early lesions of Marek's disease to the development of skin lymphomas will be undertaken. The immuno-cross reactivity of JM-V with the Marek's disease virus will be studied in reference to development of lesions and persistance of viremia.